Generally, the function of a carburetor is to supply a fuel/air mixture in a suitable proportion so as to meet the requirement of an engine under various operation conditions. Usually, a carburetor comprises a venturi; when the air flows through the venturi, the air passes through the throatlike passage will have a higher velocity to produce a vacuum sucking force so as to cause the fuel flow out of the fuel nozzle to be mixed with the air.
A carburetor with an adjustable venturi is capable of saving fuel, but it would cause the engine vacuum force to become lower upon the engine running at a high speed and load or at an ultimate speed because of the venturi being a single fuel passage member. Since the venturi is far away from the fuel outlet, the fuel would be unable to provide a sufficient horsepower; further, the total amount of gas will be limited, and therefore the performance of the engine will be lowered.
The conventional carburetor has employed a multi-fuel passage system; however, since all the venturi tubes are fixed type, they are unable to supply a suitable fuel and air mixture in suitable proportion to meet the requirement of an engine under various speeds, and therefore it is unable to have a complete combustion and to save fuel.